a＝-4。
(1)点A(1，0)关于直线z-y+1＝0的对称点是A'(a/4,-a/2)
(2)直线l1:(2+a)x+5y＝1与直线l2:ax+(2+a)y＝2垂直
A. 条件(1)充分，但条件(2)不充分。
B. 条件(2)充分，但条件(1)不充分。
C. 条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分。
D. 条件(1)充分，条件(2)也充分。
E. 条件(1)和(2)单独都不充分，条件(1)和条件(2)联合起来也不充分。
查看答案
By using the analogy of "throwing a lobster into a pot", the author tries to imply that______.
A. some managers are really foolish people
B. it's cruel to cook lobsters
C. people are tend to become complacent
D. bad environment calls for immediate action
The early American hero Benjamin Franklin is cited as______.
A. an example of squeezing more life out of his time
B. a man who loves life
C. a summary of the above statement
D. a warning to the American people
图中结构A截面的转角(顺时针为正)为()。
A. 40/El
B. 20/El
C. -20/El
D. 26.67/E1
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